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Thread: Workshop Sub-Panel Electrical (NEC) related question

  1. #1
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    Workshop Sub-Panel Electrical (NEC) related question

    Good evening all!

    I am tired of tripping my lone garage 15A circuit and running an extension cord into my mudroom, so I have decided to put a sub panel in the attached garage. I went today and got my permit, and I'm just trying to iron out a few details that are confusing me. I was a submarine electrician in the navy for 15'sh years so I have a pretty good grasp of electrical theory, checking equipment de-energized, working around live circuits, and making safe electrical connections. However, I'm still a newbie when it comes to code requirements, and I want to make sure it's safe for the wife and kids. (even though most of it seems to be common sense) I've tried calling the local inspector a few times, but I can't seem to catch him in the office.

    The goal:

    50A sub panel that is approx 75 feet from the 200A Main service equipment. New construction home, everything is less than 2 years old. I chose 50A because I already have the breaker and it keeps the cost of the feeder cable down, and I typically only run 1 piece of equipment and my dust collection at once.

    The plan:

    Install a 50A dual pole CB, run cable through the joist in the basement through the garage wall into a junction box where I will use conduit to enter the bottom of the Sub panel.

    The question:

    I understand the ground bar can't be bonded to the neutral in the sub panel. I know I need #6 copper or #4 Aluminum to run the feeder cable. My main silly question is: Does the equipment ground wire need to be insulated? I see lots of 6/3 NM-B out there, but I haven't seen 6/4. So i'm assuming I can use 6/3 NM with a ground to have my two hot conductors, neutral and the included ground wire. I'd like to use NM or other cable to be able to take advantage of the pre-engineered knockouts in my floor joist and not have to deal with conduit in the basement.

    Operating an un-grounded system my entire career, I never had to worry about it other than grounding equipment chassis to the hull of the ship .

    Thanks in advance!

    Phil
    Last edited by PHILIP MACHIN; 01-13-2020 at 6:15 PM.

  2. #2
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    the ground can be bare.

  3. #3
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    Thank you for the quick reply! Is 6/3 NM with a ground, appropriate for powering a 240 Sub Panel though?
    Last edited by PHILIP MACHIN; 01-13-2020 at 6:45 PM.

  4. #4
    6/3 nmb should be fine. Folks might try to convince you to put in 100A, as the cost isn't that much higher, but it depends on what you want and need. I have 100A wire run out to my shop, but have it on a 60A breaker in the main box, since I had it handy and 100A breakers are a bit speedy. I've never blown the 60A breaker with a 3 HP dust collector, 3 HP tables saw, lights, and AC running all at the same time.

    If you have to go through concrete wall, you'll need to sleeve the nmb with something, and it can't be used outdoors or direct bury.
    Last edited by Andrew Seemann; 01-13-2020 at 7:03 PM.

  5. #5
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    My basement ceiling is about 1 foot above the floor of my garage. So I would drill through the joist and the drywall and pass the romex right through.

    Since romex needs to be covered, I was going to pass it through the hole right into the back of a pvc junction box and then run pvc conduit up to the sub panel.

    I know romex in conduit isn’t ideal but it will only be about 3 feet until it reaches the panel. I was thinking 3/4” pvc conduit for this little run.

    I planned on using pvc conduit to run my outlets.

  6. #6
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    Phillip

    6/3 is 3 "conductors" and a bare "ground" wire. Ground is not considered a current carrying conductor per the NEC.
    The 6/3NMB will have a Black,White, and Red "conductor".

    Forward or Nuke ET(RO)?
    "The first thing you need to know, will likely be the last thing you learn." (Unknown)

  7. #7
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    Yea, I read a post where someone was claiming the bare ground in NM wasn’t sufficient to ground the sub panel. Sounded like BS but I wanted to ask to make sure.

    Nuke EMC(SS), now a Power Grid Transmission operator.
    Last edited by PHILIP MACHIN; 01-13-2020 at 9:19 PM.

  8. #8
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    2-2-2-4 Al SER cable is $1.48 per foot at HD and is good for 90 amps. 6-3 Cu NM-B (Romex) is $2.32 per foot and good for 50(?) amps. If it were me I’d use the 2-2-2-4 and a 100 amp 20 position sub panel with your existing 50 amp breaker. it gives you flexibility later on to increase the breaker size if you need more capacity.

  9. #9
    Quote Originally Posted by PHILIP MACHIN View Post
    I know romex in conduit isn’t ideal but it will only be about 3 feet until it reaches the panel. I was thinking 3/4” pvc conduit for this little run.

    I planned on using pvc conduit to run my outlets.
    Go at least 1" on the PVC to the subpannel; it is basically the same cost. 6/3 is enough of a pain to work with as it is. I'm not even sure if it will fit in 3/4 sched 40 PVC. It certainly won't do it willingly. 1" EMT would be even easier.

    If you are going to do conduit in the garage, might as well do EMT (regular metal conduit). With PVC, you have to run a separate ground wire. You're not in a submarine; it doesn't need to be waterproof PVC is kind of a pain to work with and EMT won't sag like PVC will, especially when you start hanging C clamps on it. Not that I would do that or anything. . . .

  10. #10
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    I have a full blown shop with a few 220v machines. I wanted 100a sub-panel but electrician couldn't get 100a cable into the main panel so we went with 60a. 60a works fine for a one man (sometimes 2-man) shop with a 3hp DC.
    Michael Dilday
    Suffolk, Va.

  11. #11
    Quote Originally Posted by John Lanciani View Post
    2-2-2-4 Al SER cable is $1.48 per foot at HD and is good for 90 amps. 6-3 Cu NM-B (Romex) is $2.32 per foot and good for 50(?) amps. If it were me I’d use the 2-2-2-4 and a 100 amp 20 position sub panel with your existing 50 amp breaker. it gives you flexibility later on to increase the breaker size if you need more capacity.
    Agreed. It's also going to increase resale value of the home. While most buyer's won't care about being able to run a woodshop, they will care about being able to charge their car. Generally a single fast charger for a Tesla take ~50 amps. If you've got a two car garage, then you're at 100 amps.

    Did something similar with my detached garage. Also running 2" PVC is just as easy as 1", and will allow multiple cables. You might find in the future that you're like to install solar panels on the roof of the garage, or run ethernet, or who knows?

  12. #12
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    Quote Originally Posted by Andrew More View Post
    Did something similar with my detached garage. Also running 2" PVC is just as easy as 1", and will allow multiple cables. You might find in the future that you're like to install solar panels on the roof of the garage, or run ethernet, or who knows?
    Yep, I do not like stuffing conduit. Circuits always seem to be added.

  13. #13
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    Quote Originally Posted by Andrew More View Post
    Agreed. It's also going to increase resale value of the home. While most buyer's won't care about being able to run a woodshop, they will care about being able to charge their car. Generally a single fast charger for a Tesla take ~50 amps. If you've got a two car garage, then you're at 100 amps.

    Did something similar with my detached garage. Also running 2" PVC is just as easy as 1", and will allow multiple cables. You might find in the future that you're like to install solar panels on the roof of the garage, or run ethernet, or who knows?
    If you decide to go with the 2-2-2-4 SER @ 0.956” diameter, then 1 1/4” conduit is minimum @about 50% fill (bundled cables are counted as one conductor and max for 1 conductor is 53%). That would leave no room for any additional cables. Solar or maybe a genset inlet are possibilities; low voltage cables are not run in the same raceway as regular voltage.

    If you decide to go with NM-B 6/3 wg @.659”, then minimum conduit is 1” @ about 41% fill. Still not enough to ever add anything.
    Comments made here are my own and, according to my children, do not reflect the opinions of any other person... anywhere, anytime.

  14. #14
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    Thanks for all the feedback,

    If I use 1 inch sch 80, can I run a 120 circuit and 240 circuit in the same conduit? I wanted to T off at the end and have the two outlets near each other. It would be 12 awg thhn for the 120 and 10 awg for the 240.

  15. #15
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    Check craig's list for wire and cable. Folks are often selling big wire for 1/2 the the box stores. Saves money even if you end up with cable bigger then you need. Consider one panel at each end of the shop to save wire cost.
    Bill D.

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